1. Field of the Invention
This invention relates to a method and apparatus for efficiently utilizing and recovering heat utilizing a decomposing reaction of methanol that generates reformed gas (hereinafter referred to as "endothermic reform reaction") and synthesizing reaction of reformed gas to produce methanol (hereinafter referred to as "exothermic reform reaction") for simplifying the transportation of recovered heat together with a simple wide area transport of heat in the form of methanol and reformed gas by providing pipelines that extend over a wide area for the delivery of methanol and reformed gas.
2. Description of the Prior Art
Previously heat recovery, utilization and transportation, have been limited to relatively localized areas and such transportation, utilization and recovery operations have been implemented separately. Moreover, recovered waste heat and recovered heat discharged at designated locations is reutilized at the same place that the heat was first utilized and recovered. It is extremely difficult to transport such heat to remote areas for utilization, and the heat efficiency is poor. In addition, owing to the difficulty of ensuring the economic efficiency, heat transportation and utilization using piped hot-water and steam has been limited to a distance of some several kilometers, and over greater distances has been virtually non-existent.
A method is known in which a carbon oxide based endothermic reform reaction is utilized to supply a fuel cell with hydrogen produced from methane. This method uses a relatively high temperature (300 to 800 degrees) heat source. Also known are heat recovery systems in which heat discharged by a combustion means is used to preheat the air used in the combustion process or for heating a fluid. Also known are systems which apply waste heat energy to effect the transfer of fluids or gases, or in which the waste heat medium itself is transferred for recovery and reutilization.
Moreover, from the viewpoint of heat utilization efficiency and heat utilization format, in using waste heat utilization and recovery it is desirable that the original exergy (concerning which, see below) be improved, but in the case of conventional heat utilization methods and systems this has not been done and, therefore, efficient utilization has not been possible.
The concept of exergy will now be explained. From the viewpoint of the quality of heat energy utilization, it is not enough to discuss just the total amount of energy; instead, it must be discussed in terms of the amount of energy that can be converted into work (which energy shall hereinafter be referred to as "exergy") or "available energy."
Here, exergy A signifies the maximum amount of work that can be obtained from that energy, which in a fluid system can be defined by the following equation. EQU A=H-H.sub.o -T.sub.o (S-S.sub.o)
Here, H is enthalpy, S is entropy and T is absolute temperature, and the subscripted characters indicate the state of the surrounding environment.
The energy Q possessed by this fluid system state is EQU Q=H-H.sub.o.
Based on the law of the conservation of energy in accordance with which heat exchange or heat conversion does not change the total amount of energy, a discharge of energy by a system results in a loss of enthalpy and energy, but the energy of the receiving side increases by the amount of energy received. However, the reduction in exergy A brought about by this transfer of energy will always be larger than the amount of increase in the exergy of the receiving side. That is, while the total amount of energy Q is always conserved, the total amount of exergy A will continue to decrease with the transfer of the energy.
Here we shall consider the proportion of the total amount of energy that can be converted into exergy. As the exergy will continue to decline while the total amount of energy remains constant, we can say that the ratio of exergy to the energy possessed by a substance represents the quality of the energy of that substance. We shall call the value that represents this energy quality the exergy ratio .eta.. That is, if P is pressure, in a gas where T&gt;T.sub.o and P=P.sub.o, the exergy ratio .eta. is obtained by the following equation. EQU .eta.=1-T.sub.o (S-S.sub.o)/(H-H.sub.o).
Generally when we consume energy, more accurately it means that we are consuming exergy, and the exergy ratio .eta. decreases with each consumption. Considered from the viewpoint of this exergy, fossil fuel can be termed a higher-quality (higher exergy ratio) fuel than hydrogen, while considered from the viewpoint of this exergy, waste heat is a lower-quality (lower exergy ratio) energy than hydrogen.
In recovering and reutilizing waste heat energy, it is preferable to raise the exergy ratio for recovery purposed. In order to accomplish this it is necessary to supply from somewhere an amount of exergy that is more than the amount by which the exergy needs to be increased.
With the decomposition by endothermic reaction of a hydrocarbon into hydrogen and carbon monoxide or carbon dioxide means that hydrogen, a low exergy ratio fuel, is generated from hydrocarbon, a fuel having a high exergy ratio, which from the viewpoint of the effective utilization of heat energy is not desirable. On the other hand, however, the carbon dioxide generated by the reform reaction can be easily recovered without being released into the atmosphere and, moreover, the generation of hydrogen, a clean fuel, means that a fuel is thus obtained that is effective in environmental terms. And, if waste heat is used to obtain the necessary heat for the endothermic reform reaction, it means that waste heat having a low exergy ratio can be raised to the higher exergy ratio of hydrogen.
As mentioned, previously methods and systems for the recovery, utilization and transportation of thermal energy have been limited to relatively localized areas and such transportation, utilization and recovery operations have been implemented separately. Also, transporting such heat a substantial distance, such as several tens of kilometers, has been difficult and the loss so great that it has not been practiced to any real extent.
Also, in the case of the conventional method that utilizes a carbon oxide based endothermic reform reaction, the heat source used in the reaction is a relatively high temperature one (300 to 800 degrees). To apply waste heat for this reaction would therefore mean having to use waste heat at such a high temperature that, in practical terms, it would be difficult to utilize waste heat produced by a factory or generated in the region.
In general systems that utilize waste heat energy only use it to preheat air used in a combustion process, or to heat a fluid, and are not set up to raise the exergy ratio of waste heat for recovery and reutilization. Also, when waste heat energy is used to be transferred to another place for utilization, this can only be done by shifting the energy into a gas or fluid which is then moved, or by moving the waste heat medium itself, a procedure which inevitably is accompanied by a large loss of the energy from thermal radiation.